1. Field of the Invention
The present invention relates to an optical pickup device and an optical disc apparatus and is suited for use in, for example, an optical pickup device and optical disc apparatus that are compatible with multi layer optical discs.
2. Description of Related Art
Generally, an optical disc apparatus equipped an optical pickup device is used to read information from, and write information to, an optical disc. This optical pickup device performs, for example, focus adjustment by changing the position of an objective lens in a focus direction based on a focusing error signal detected by detection parts of a detector and also performs tracking adjustment by changing the position of the objective lens in an optical disc radial direction (hereinafter referred to as the radial direction) based on a tracking error signal in order to accurately emit a spot on a specified track in the optical disc. A conventional optical disc apparatus performs position control of the objective lens based on a servo signal by means of the focusing error signal and the tracking error signal.
Meanwhile, multi layer optical discs, each of which has a plurality of information recording layers, have been known in recent years along with the popularization of large-capacity optical discs. When reading information from, and writing information to, a multi layer optical disc composed of three or more information recording layers by using a conventional optical pickup device, there is a possibility that signal light reflected from an information recording layer and a stray light reflected from another information recording layer may enter the same detection part of a detector. In this case, the resulting problem is that the signal light and the stray light interfere with each other and, therefore, an accurate tracking error signal cannot be detected and stable tracking control can no longer be performed.
As a means for solving the above-described problem, for example, Japanese Patent Application Laid-Open (Kokai) Publication No. 2008-135151 discloses a method for detecting a stable tracking error signal while avoiding the stray light reflected from the other information recording layer(s), by locating a detection part for detecting the tracking error signal at a position away from the stray light, further locating some detection parts along a direction of an extension line of a tangent relative to the track of the optical disc (hereinafter referred to as the tangential direction), and locating the remaining detection parts in the optical disc radial direction (radial direction) perpendicular to the tangential direction of the track.